During the operation of a vortex flow sensor of this kind, a Karman vortex street is, as is known, formed downstream of the bluff body, and the pressure fluctuations of this street are converted by a vortex sensing element into an electrical signal, the frequency of which is proportional to the volume flow rate.
GB Patent 1,483,818 describes a vortex flow sensor for measuring the flow velocity or volume flow rate of a fluid flowing in one direction of flow in a measuring tube
with a bluff body which is arranged along a diameter of the measuring tube and serves to generate Karman vortices and PA1 with a vortex sensing element which responds to pressure fluctuations generated by the vortices, is inserted into a wall opening of the measuring tube downstream of the bluff body, sealing off this opening relative to the circumferential surface of said measuring tube, and is shorter than the diameter. PA1 with a bluff body which is arranged along a diameter of the measuring tube, is connected at each end to the measuring tube, serves to generate Karman vortices and has a main hole, running in the direction of this diameter and through the measuring tube, and at least one secondary hole, which connects the main hole to the fluid, PA1 with a capacitive vortex sensing element which responds to pressure fluctuations generated by the vortices, is inserted into the main hole, sealing off the latter from the fluid, and has the following features: PA1 with a vortex sensing element which is inserted into a wall opening of the measuring tube, sealing off this opening relative to the circumferential surface of said measuring tube, and has the following features: PA1 with a bluff body which is arranged along a diameter of the measuring tube, is connected to the measuring tube at at least one fixing location and serves to generate Karman vortices, PA1 with a capacitive vortex sensing element which responds to pressure fluctuations generated by the vortices, is inserted into a wall opening in the measuring tube downstream of the bluff body, sealing off this hole relative to the circumferential surface of said measuring tube, and the center of which lies, together with the center of the fixing location, on a generatrix of the measuring tube, and has the following features: PA1 with a bluff body which is arranged along a diameter of the measuring tube, is connected to the measuring tube at at least one fixing location, serves to generate Karman vortices and has a main hole, running in the direction of this diameter and through the measuring tube, and at least one secondary hole, which connects the main hole to the fluid, PA1 with a capacitive vortex sensing element which responds to pressure fluctuations generated by the vortices, is inserted into the main hole, sealing off the circumferential surface of the measuring tube from the fluid, and has the following features:
U.S. Pat. No. 4,716,770 describes a vortex flow sensor for measuring the flow velocity and/or volume flow rate of a fluid flowing in one direction of flow in a measuring tube
a flexible outer sensor sleeve which is closed at the ends and serves as a first electrode, and PA2 a flexible inner sensor sleeve which is arranged therein and carries at least one second electrode at the end. PA2 a bearing which is thinned to a diaphragm in the area of the opening, covers the opening and has a first surface facing toward the fluid and a second surface facing away from the fluid, PA2 a first end of a flexurally stiff beam is attached to the first surface of the diaphragm, PA2 a second end of the beam is attached to the second surface of the diaphragm, PA2 a sensor element sensing movements of the second end of the beam is attached to a housing and cooperates with the second end, PA2 a diaphragm which covers the opening and which has a first surface facing toward the fluid and a second surface facing away from the fluid, PA2 a flexurally stiff thin sensor vane is attached to the first surface of the diaphragm and is shorter than the diameter, having flat main surfaces which are in alignment with the generatrix of the measuring tube, PA2 a sleeve-shaped first electrode arrangement is attached to the second surface of the diaphragm and comprises at least one electrode, PA2 a housing cap which surrounds the first electrode arrangement and the diaphragm, is fixed on the measuring tube and contains a second electrode arrangement with at least one counterelectrode, PA2 the mass of the sensor vane is made greater than the mass of the first electrode arrangement, PA2 the geometrical moment of inertia of the sensor vane at the first surface of the diaphragm is made approximately equal to the geometrical moment of inertia of the first electrode arrangement at the second surface of the diaphragm, and PA2 the housing cap is dimensioned to be of sufficient flexural stiffness to ensure that it does not bend in the case of a maximum permissible acceleration acting on the measuring tube. PA2 a diaphragm which covers a measuring-tube end of the main hole and which has a first surface facing toward the fluid and a second surface facing away from the fluid, PA2 a flexurally stiff sensor sleeve is attached to the first surface of the diaphragm, PA2 a sleeve-shaped first electrode arrangement is attached to the second surface of the diaphragm and comprises at least one electrode, PA2 a housing cap which surrounds the first electrode arrangement and the diaphragm, is fixed on the measuring tube and contains a second electrode arrangement with at least one counterelectrode, PA2 the mass of the sensor sleeve is made equal to the mass of the first electrode arrangement, PA2 the geometrical moment of inertia of the sensor sleeve at the first surface of the diaphragm is made approximately equal to the geometrical moment of inertia of the first electrode arrangement at the second surface of the diaphragm, and PA2 the housing cap is dimensioned to be of sufficient flexural stiffness to ensure that it does not bend in the case of a maximum permissible acceleration acting on the measuring tube.
The disclosure in U.S. Pat. No. 4,716,770 is hereby incorporated by reference and made part of the specification in this application.
Finally, EP-A 549 945 describes a vortex flow sensor for measuring the flow velocity and/or volume flow rate of a fluid flowing in one direction of flow in a measuring tube
the ends are so dimensioned that they perform opposite and equal torsional moments to the diaphragm.
As the GB Patent 1,483,818 and the U.S. Pat. No. 4,716,770 both referred to indicate, the vortex sensing element can be arranged either in the bluff body or, separately from the latter, in the opening in the wall of the measuring tube. With regard to cost reduction in the production of the vortex flow sensor, on the one hand, and with regard to the standardization of the components of the latter, on the other hand, a vortex sensing element which can be inserted not only into the bluff body (as in U.S. Pat. No. 4,716,770) but also into the wall of the measuring tube (as in GB Patent 1,483,818) is desirable.